1. Field of the Invention
The present invention relates to a motion control system for moving a moving body by a desired amount of movement, e.g., a motion control system such as a goniometer for causing a rotating body to rotate by a desired angle. The present invention also relates to an X-ray measurement apparatus comprising the motion control system of above description.
2. Description of the Related Art
Motion control systems for moving a moving body by a desired amount of movement are widely used in a variety of industrial sectors, such as machine tools, motor vehicles, robots, measurement instruments, and other fields. For example, in the field of measurement instruments, a goniometer, which functions as a motion control system, is sometimes used to cause a rotary stage to rotate in an instance in which the rotary stage, which functions as a moving body and which supports a specimen to be measured, is caused to rotate by a desired angle.
A goniometer of such description has, e.g., an electric motor, which functions as a power source for causing the rotary stage to rotate, and an angle detector for detecting the angle of rotation of the rotary stage. Conventionally known angle detectors of such description include that disclosed in Patent Citation 1. In this angle detector, one angle data detection head, which functions as a reference; and a plurality of nth degree error component detection heads are arranged around a rotating disc; respective output data from each of the nth degree error component detection heads is applied to a predetermined computation formula to obtain an nth degree error component; the nth degree error component is subtracted from output data from the reference head; whereby the output data is calibrated and highly accurate angle data having minimal error is obtained. Patent Citation 1 also discloses a technique in which a table, comprising the nth degree error components and angle values, is utilized according to need.
Patent Citation 1 does not mention methods for utilizing calibrated angle data that has been obtained as described above. One general method of utilizing calibrated angle data of such description is a processing system such as that shown in FIG. 14, in which a common personal computer is used. In this system, a plurality of detection heads 102a through 102d, including a reference detection head 102a, are arranged at appropriate angular intervals around an encoder disc 101 provided with a calibration (i.e., a scale).
The encoder disc 101 is integrally connected to a rotating body (not shown), the rotating body being driven by a servo motor 109, which is an electric motor. The encoder disc 101 rotates integrally with the rotating body. The angle of rotation of the servo motor 109 is controlled by a servo amplifier 108. The servo amplifier 108 controls the angle of rotation of the servo motor 109, based on an angle instruction signal S0 sent from a controller 107. The controller 107 transmits an angle signal Sa to a second personal computer 110.
An analog output signal from each of the detection heads 102a through 102d is converted into a digital signal by an analog-digital converter (ADC) 103, and is subjected to an n-fold increase in frequency by an interpolator 104 (i.e., n-fold interpolation). Data after interpolation is subjected to predetermined computation by a personal computer 105, data for calibration is obtained, and the data for calibration is transmitted to the second personal computer 110. The personal computer 110 creates a calibration table 106 based on the transmitted data.
The second personal computer 110 calibrates, using the calibration data stored in the angle calibration table 106, the angle signal Sa sent from the controller 107. The calibrated angle data is deemed to be the correct angle data. The correct angle data is reflected on, e.g., a screen of a display 111, which is an output instrument. The method for utilizing the angle calibration table 106 shown in FIG. 14 is an example, and a variety of other utilization methods can be envisaged.
In general, in an instance in which there are a plurality of angle data processing systems shown in FIG. 14, even if the mechanical and electrical constituent elements that form each of the systems are completely identical, characteristics of the assembled angle data processing systems will be inconsistent. Therefore, calibration data stored in the angle calibration table 106 is different between each of the angle data processing systems.
Also, mechanical and electrical characteristics of the angle data processing systems change over time. Therefore, as a rule, the content of the angle calibration table 106 must be modified over time. Also, in an instance in which, as an option, an auxiliary load is placed on the moving body (e.g., a rotary stage) onto which the encoder disc 101 is mounted, the moving body may deform as a result of unbalanced load, and the angle calibration table 106 must be re-created each time this occurs.
As described above, calibration data in the angle calibration table 106 must be created for each angle control system, and even data for a single control system must be modified over time. Management of the angle calibration table 106 is extremely troublesome.
A conventional angle detector, similar to the angle detector used in the angle data processing system shown in FIG. 14, is disclosed in Patent Citations 2 and 3. Patent Citation 3 is a U.S. patent specification based on Patent Citation 2. In these patent citations, there is disclosed an angle data processing system in which one second calibration-reading head, which represents a reference, and a plurality of first calibration-reading heads are arranged around a calibration plate, which corresponds to an encoder disc. In this processing system, a difference in measurement between the single second calibration-reading head and each of the first scale reading heads is obtained; an average of the differences is obtained; a calibration curve is obtained based on the average of the differences; the calibration curve is used to calibrate the output data of the second calibration-reading head, which is the reference; and the calibrated data used as the final angle data.
Patent Citations 2 and 3 do not mention methods for utilizing the calibrated angle data obtained as described above. In general, an angle data processing system such as that described further above and shown in FIG. 14, i.e., a system for performing a process in which the angle signal Sa from the controller 107 is calibrated using the angle calibration table 106 and outputted when required, can be envisaged.    [Patent Citation 1] JP-A 2003-262518 (pages 2 and 3, FIGS. 1 through 4)    [Patent Citation 2] JP-A 2006-098392 (pages 3 through 5, FIG. 1)    [Patent Citation 3] U.S. Pat. No. 7,143,518